Types of Yams

While the rest of the world may understand tubers, a fateful decision made by agricultural marketers to differentiate two kinds of sweet potatoes — calling one variety "yam" and the other "sweet potato" — has bedeviled American consumers ever since, especially at Thanksgiving.

The reality is that almost all of the non-white potatoes sold in United States supermarkets are sweet potatoes, which means they are members of the morning glory (Ipomoea) family. True yams belong to an entirely different species, the lily (Dioscorea) family.

But, in practice, one type of the orange-fleshed spud sold in the U.S. is known as a "sweet potato," while the other U.S. sweet potato category is colloquially known as the "American yam." It's only in specialty markets that you'll likely find true white or even purple yams. Many of these varieties of yam are from elsewhere in the world, and all have unique properties. It's worth seeking them out and trying the recipes for which each yam type is known.

But whatever name you call it, the color of your yam or your sweet potato's inner flesh may help you decide which type to get. White potatoes and white yams do possess some nutritional advantages. They're a little higher in potassium than their more colorful brothers and sisters and a bit higher in fiber. But it's the yellow, orange and purple-hued types of yams and sweet potatoes that are bursting with antioxidants like vitamins A and C, as well as complex carbohydrates.

The "yams" that Americans buy during the holiday season are actually one of the two main types of sweet potatoes (I. batatas). But no list of yams would be complete without including the "faux yam" sold in U.S. markets. The types of sweet potatoes labeled as yams in the U.S. are differentiated from other varieties by their softer flesh, reddish-copper outside color and bright orange color on the inside. "Regular" sweet potato types, in contrast, are paler inside and out, and they have firmer flesh.

The American yam sweet potato varieties sold in supermarkets most often are named "beauregard," "jewel" and "garnet." Most importantly, when cooked, American yam sweet potatoes have a light, creamy texture. That's why they are superior to the firm group of sweet potatoes when it comes to making a basic baked potato with the "jacket" on.

Of course, American yam sweet potatoes are also known for their ability to transform into holiday side dishes. Whether you like them candied with marshmallows or topped with pecans and brown sugar, the soft American yam sweet potatoes are superior to firm sweet potatoes when it comes to these dishes.

The Japanese mountain yam (D. japonica) is also known as yamaimo or nagaimo. This imported yam is shaped like a cylinder, with pale, "hairy" skin. The flesh itself is white. Yamaimo is often classified as a "sticky" yam, but "slimy" would be a somewhat more accurate term.

As unappealing as "slimy" or "mucilaginous" might sound, it can be a prized quality in the kitchen, similar to American okra. Just as okra helps thicken dishes like gumbo, yamaimo binds savory Asian pancakes, adds substance to a radish-soy sauce broth or thickens any noodle bowl dish. In these cases, grating or julienning the Japanese mountain yam is the most efficient way to add it to cooked dishes.

The traditional way to use uncooked yamaimo is to thinly slice the peeled yam and add it to a fresh Japanese salad. Toss it with salad greens, shaved carrots and orange slices, and dress the salad with a bottled Japanese dressing. Alternatively, mix up a homemade dressing incorporating ginger, soy sauce and rice wine vinegar.

Like many other globally famous vegetables, tropical yam (D. trifida) goes by several other names, including true yam, Indian yam, name, cush-cush, kush kush, yampi, mapuey, yampi and igname. It grows in tropical regions, including those in Asia, Africa and Latin America.

Many tropical yam cultivars have thickened skins with cracks, like bark, or large clefts on one end. Their flesh is dry, firm and white. The tubers produce vines that grow up to 10 feet long, with green flowers and tiny fruit capsules. Tropical yams have a dry texture and a fairly bland taste, but the dishes in which they're commonly used are designed to give them flavor.

In the Caribbean, mashed kush kush is a favorite comfort food in which the cooked, mashed yams are mixed with a sauteed blend of onions, hot peppers, herbs and seasonings to give the yams more moisture and flavor. In West Africa, the tropical yam is included in a hearty stew known as ragout d'igname. Browned cubed beef, tomatoes and onions simmer in beef broth sauce. The peeled, cubed yams are added, then boiled with the other ingredients for about a quarter of an hour.

Ube (Dioscorea alata) is having a bit of a moment these days. These bright purple yams, also known as "Filipino yams," have hit the U.S. market in a big way, thanks to the vivid hue they lend to desserts. Ube's flesh ranges from mottled white and purple to solid lavender, and its skin is thick, brown and heavily ridged.

Rather than using fresh yams, modern "Pinterest-style" ube recipes start with prepared products such as ube powder. Ube powder turns into a paste-like substance when boiled with water, making it ready to create purple cake and purple cupcake batter, homemade purple ice cream mixtures and other violet-colored baked goods.

Of course, many traditional recipes use whole ube yam rather than an ube product. Ube candy combines cooked, riced ube yam flesh with condensed milk and lime zest, which is cooked, then rolled into logs and sugared. Ube halaya, a traditional Filipino dessert pudding, blends cooked, mashed ube yam flesh, condensed milk, evaporated milk, butter and sugar, cooked until thickened, then chilled.

Halo-halo, a creamy layered dessert popular in restaurants and from street vendors, starts with shaved ice flavored with ingredients like coconut gel and red mung bean paste, then topped with purple ube halaya.

Air potatoes (D. bulbifera) are true yams that are cultivated in the U.S. and other parts of the world. Currently only sold as a specialty crop in American markets, air potatoes are too often labeled a garden pest instead of a food source. That's because their vines grow aggressively — as much as 8 inches a day. Yet this versatile tuber deserves to be better known, especially because it's a rare domestic version of a true yam.

The air potato vine produces edible tubers both above and below ground. It's important to only buy or grow cultivars labeled as edible, because some wild types can be poisonous. The tubers are about 5 inches long, and they're either roundish or oval. The light-orange flesh is firm but slimy, similar to okra. Boil them before using them to remove their bitter taste.

Because air potatoes are better appreciated from a culinary standpoint in Asia, many of the better-known recipes featuring them hail from the East. Their "slimy" texture makes them ideal binders for okonomiyaki, savory Asian pancakes. They also thicken nimono, a Japanese dish in which starches, other vegetables and meats are slowly simmered in dashi broth.

Like ube, Okinawan yam (I. batatas), also known as Okinawan purple potato, shows up in ice cream and dessert dishes ‒ especially in Hawaii, where it's a staple vegetable. (The "Okinawa" reference comes from the Japanese imported spud introduction to Hawaii by way of Polynesian travelers.) The Okinawan yam is equally at home in savory dishes as well as sweet ones.

The tuber, although botanically speaking, a sweet potato, is nicknamed both "Okinawan yam" and "Okinawan sweet potato." It has light copper skin and an oblong shape reminiscent of American sweet potatoes. But once cut open, the tuber's flesh reveals itself to be intensely purple. While it's mostly grown and sold in Hawaii, you may be able to find it in specialty markets in the contiguous United States.

The Hawaiian equivalent of Southern candied yams, mashed purple Okinawan yams feature coconut milk, sea salt, garlic and a bit of Hawaiian sweet sauce. The dish makes an intriguing addition to any family gathering. As with other tubers, roasting cubed Okinawan yams brings out some sweetness to pair with their savory side. The yam can also be thinly sliced, dipped in tempura batter and fried.

Chinese yam (D. polystachya) is also known as "cinnamon vine" for its ornamental, cinnamon-scented white flowers. The yams themselves have a tube-like shape, bark-like skin and bright white flesh. Chinese yam is unlike most other types of yams in that it prefers colder, elevated regions to tropical climates.

Chinese yam is used widely in Chinese medicine, but it also has its uses as a starchy vegetable. Use it as you would a white potato. It can be baked, roasted or added to stews and casseroles. It has a mild flavor and firm flesh.

Chinese cooks also follow a culinary tradition of slicing this delicately flavored yam into thin slices and pickling it for storage. Other uses of uncooked Chinese yam include shredding it like a cabbage to make a marinated side dish.

Two types of yams dominate the West Africa starchy vegetable group — the white guinea yam (D. rotundata) and the yellow guinea yam (D. cayenensis). Both are large, weighing about 4 to 6 pounds. Each type also has bark-like skin. As their names suggest, white guinea yam has white flesh, while the skin of a yellow guinea yam is light yellow.

If you come across both of these species in the specialty market, choose them based on the dish you'd like to make. White guinea yams are similar to white baking potatoes and are softer and fluffier than the African yellow varieties of yam when cooked. Use them as a substitute for mashed or roasted potatoes.

Yellow guinea yams hold up well in stews when cubed and peeled. Alternatively, boil and mash the peeled spuds; then deep-fry them as dumplings. They can also be baked and eaten like sweet potatoes.

A favorite tuber of India and southern Vietnam, among other places, the lesser yam (D. esculenta) is also known as the Chinese yam. The oval tubers are on the small side, weighing between a 1/2 to 2 pounds on average. The outer skin is brown and somewhat hairy, with white or pale yellow flesh.

This sweet-tasting yam can be cooked as you would white or sweet potatoes. Mash the peeled tubers after boiling; then season them to taste. Alternatively, bake them whole like jacket potatoes, or peel and roast them in chunks.

Lesser yam's natural sweetness also makes it a natural for Asian versions of sweet potato desserts. One such dish is che cu tu, (Vietnamese lesser yam pudding). The cubed yam chunks are boiled until tender, then cooked with sugar and tapioca starch.